Method of making a turbine regenerative seal

ABSTRACT

A thin, compliant seal for the regenerator of a gas turbine engine or the like and a method of making same. The seal is comprised of a plurality of individual seal elements that are interrelated with each other at their ends to preclude leakage. Two embodiments of end relationships are shown. In one embodiment two of the seal elements have interengaging portions that provide a loose connection between the elements. In the other embodiment, each of the seal ends carries a locating portion that coacts with means on the housing of the regenerator for providing a loose interrelationship between the seal ends. The end interrelationship of the seal elements in each embodiment permits relatively free movement of the seal elements under the influence of thermal expansion. This precludes warping of the seal as would occur if the seal were constructed from a single piece or if the seal was formed from pieces that were rigidly connected to each other. Each of the seal elements includes a first relatively thin, compliant part that is provided with a wear resistant coating that engages a rotating element. The coating is applied to a lightly oxidized surface of a relatively thin substrate which substrate is unstressed to reduce warpage. Cantilevered springs form another piece of each element. These cantilevered springs sealingly engage a static mating surface of the regenerator and resiliently bias the coated surface first piece into sealing engagement with the rotating element. The coating, as has been noted, is applied to an oxidized surface of the first part. In a preferred embodiment the coating is applied after the cantilevered spring is assembled to the first part. This subassembly is then held in a fixture and is preheated. A relatively thin transition layer of coating material is applied to the oxidized surface. The transition coating is formed from a material that will have an exothermic reaction with the oxidized surface. The final, wear resistant coating is then applied to the transition coating while maintaining the temperature and preventing excessive heating and, accordingly, warpage. The use of a thin seal and relatively thin coatings insures compliance of the seal with the mating surface of the rotating element.

United States Patent [1 1 Good et al.

[ Dec. 30, 1975 METHOD OF MAKING A TURBINE REGENERATIVE SEAL [75] Inventors: William E. Good, Cinnaminson,

N.J.; Leonard Di Grasso, Philadelphia, Pa.; James D. Hoffman, Santa Monica, Calif.

[73] Assignee: Kelsey-Hayes Company, Romulus,

Mich.

[22] Filed: Mar. 8, 1973 [21] Appl. No.: 339,123

Related U.S. Application Data [62] Division of Ser. No. 231,975, March 6, 1972, Pat.

[52] US. Cl. 29/460; 148/635; 427/34; 427/226; 427/301; 427/318 [51] Int. Cl. C23c 7/00 [58] Field of Search 117/50, 71 M, 105.2, 105, 117/127; 148/635; 29/460; 427/34, 226,

3,552,370 1/1971 Briggs 117/105 3,700,505 10/1972 Kanter 117/50 3,743,008 7/1973 Zeek et al 427/34 3,758,124 9/1973 Weinberger et al. 117/105.2

Primary ExaminerRalph S. Kendall Assistant Examiner-John D. Smith Attorney, Agent, or FirmI-Iarness, Dickey & Pierce [57] ABSTRACT A thin, compliant seal for the regenerator of a gas turbine engine or the like and a method of making same. The seal is comprised of a plurality of individual seal elements that are interrelated with each other at their ends to preclude leakage. Two embodiments of end relationships are shown. In one embodiment two of the seal elements have interengaging portions that provide a loose connection between the elements. In the other embodiment, each of the seal ends carries a locating portion that coacts with means onthe housing of the regenerator for providing a loose interrelationship between the seal ends. The end interrelationship of the seal elements in each embodiment permits relatively free movement of the seal elements under the influence of thermal expansion. This precludes warping of the seal as would occur if the seal were constructed from a single piece or if the seal was formed from pieces that were rigidly connected to each other. Each of the seal elements includes a first relatively thin, compliant part that is provided with a wear resistant coating that engages a rotating element. The coating is applied to a lightly oxidized surface of a relatively thin substrate which substrate is unstressed to reduce warpage. Cantilevered springs form another piece of each element. These cantilevered springs sealingly engage a static mating surface of the regenerator and resiliently bias the coated surface first piece into sealing engagement with the rotating element. The coating, as has been noted, is applied to an oxidized surface of the first part. In a preferred embodiment the coating is applied after the cantilevered spring is assembled to the first part. This subassembly is then held in a fixture and is preheated. A relatively thin transition layer of coating material is applied to the oxidized surface. The transition coating is formed from a material that will have an exothermic reaction with the oxidized surface. The final, wear resistant coating is then applied to the transition coating while maintaining the temperature and preventing excessive heating and, accordingly, warpage. The use of a thin seal and relatively thin coatings insures compliance of the seal with the mating surface of the rotating element.

9 Claims, 10 Drawing Figures US. Patent Dec. 30, 1975 Sheet 2 of 3 US. Patent Dec. 30, 1975 Sheet3 of3 3,928,906

METHOD OF MAKING A TURBINE REGENERATIVE SEAL This is a division of application Ser. No. 231,975, filed Mar. 6, 1972, issued Sept. 25, 1973, as US. Pat. No. 3,761,101.

BACKGROUND OF THE INVENTION This inventionrelates to a seal and more particularly to an improved seal that is particularly adapted for use in .a regenerator of a gas turbine engine and a method of making such a seal. 1

Seals for turbine engines are required to function adequately under extreme conditions. There are considerable temperature gradients in such an application that impose considerable thermal stresses on a seal. Heretofore the differing thermal expansion to which the seal was subjected resulted in poor sealing characteristics.

It is, therefore, a principal object of this invention to provide an improved seal for a turbine engine or thelike.

It is another object of the invention to provide a seal for a turbine engine that is not adversely effected by temperature gradients.

The types of seals generally used in turbine engines have been of a single piece construction. It has been found that the adverse effects of temperature gradients may be minimized by using a multi-piece seal construction. With such an arrangement, however, it is necessary to insure good sealing at certain of the junctures between the seal pieces.

It is, therefore, a further object of this invention to provide a multi-piece seal that insures good sealing at the seal junctures.

It has been found that sealing may be improved by employing a seal element that is relatively thin and compliant. Such a sealing element will effectively seal surfaces that become distorted due to temperature variations. However, for a variety of reasons the previously proposed seals for turbine engines have not been thin and compliant. One reason is that the seals have been provided with wear resistant coatings. For the most part metal oxides have been used for this purpose. These oxides are inherently fragile and it was thought necessary to provide a thick and rigid member as the supporting substrate. Also, the methods of applying the coatings to these substrates previously used required thick substrates. It was thought necessary to remove the metal oxides from the substrate. by shot blasting or other similar procedure. These procedures introduce surface stresses which can cause distortions under thermal loading.

It is, therefore, another object of this invention to provide a thin, compliant seal for a turbine engine.

It is a further object of the invention to provide a thin, compliant coated seal.

It is yet another object of this invention to provide an improved method of coating a seal with a wear resistant material.

SUMMARY OF THE INVENTION A feature of this invention is adapted to be embodied in a seal for a regenerator of a gas turbine engine or the like. The seal includes a first seal member having an arcuate configuration and a second seal member having end portions juxtaposed to the end portions of the first seal member. The first and second seal members each have sealing faces that lie in substantially the same plane and which are adapted to sealingly engage a portion of the engine around at least one of its gas flow paths. Means are provided for locating the contiguous ends of the seal members relative to each other and for allowing relatively free movement of the ends for permitting independent thermal expansion of the seal members.

Another feature of this invention is adapted to be embodied in a seal for a regenerator of a gas turbine engine or the like. The seal includes a first seal member that is relatively thin and compliant and which has a surface that is adapted to sealingly engage a first portion of the engine. Resilient biasing means sealingly engage a second portion of the engine and urge 'the surface of the first member into sealing engagement with its respective portion of the engine.

Yet another feature of this invention is adapted to be embodied in a method of applying a wear resistant coating to a metal substrate for forming a compliant seal. The method comprises the steps of preheating a substrate having a lightly oxidized surface and deposit- .ing a transition coating on the oxidized surface. The

transition coating is formed from a material which exothermically reacts with the oxidized surface of the substrate to form a good surface bond. The wear resistant coating is then deposited upon the transition coatmg. I

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is anend elevational view of a first embodiment of a seal for the regenerator of a gas turbine engme.

FIG. 2 is an enlarged cross sectional view taken along the line 2-2 of FIG. 1.

FIG. 3 is an enlarged cross sectional view taken along the line 3-3 of FIG. 1.

FIG. 4 is an enlarged cross sectional view taken along the line 4-4 of FIG. 1.

FIG. 5 is an-enlarged elevational view of the area encompassed by the circle 5 in FIG. 1.

FIG. 6 is a still further enlarged view of the structure shown in FIG. 5, with portions broken away.

FIG. 7 is an enlarged cross sectional -view taken along the line 7-7 of FIG. 5.

FIG. 8 is a view, in part similar to FIG. 5, and shows a second embodiment of the invention.

FIG. 9 is an enlarged view, with portions broken away, of the area shown in FIG. 8.

FIG. 10 is an enlarged cross sectional view taken along the line 10 -10 of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A seal constructed in accordance with a first embodiment of this invention is shown in FIGS. 1 through 7 and is identified generally by the reference numeral 11. The seal 11 is particularly adapted for use in a gas turbine engine and specifically for sealing the housing relative to the rotating core of the gas regenerator. The seal, therefore, experiences considerable temperature and pressure differences, as will be explained further in this description. The seal is particularly flexible and compliant so as to work effectively under these adverse conditions.

The seal 11 is comprised of three sub assemblies or seal pieces. These pieces include a first, generally arcuate shaped piece 12, a second generally straight piece 13 and a third generally arcuate shaped piece 14. The ends of the seal pieces 12, 13 and 14 are interrelated with each other in such a manner as to permit independent thermal expansion of each piece relative to the others. The interconnection between the ends of the seal pieces 12, 13 and 14, however, is such as to provide an effective seal at the juncture.

As will be readily apparent from an inspection of FIG. 1, the assembled seal 11 has a generally circular shape and the seal piece 13 intersects the circle along a cord so as to provide a lower flow path 15 and an upper flow path 16. When assembled in the engine the gases flow from the compressor through the rotating core (not shown) out of the flow path 15 as viewed in this Figure. The gases flowing in the area of the flow path 15 have a relatively high pressure and an elevated temperature. The gases that leave the flow area 15 pass through the combustor, the turbine and then return through the rotating core entering via the flow path 16. At this point, the gases will have a substantially lower pressure, approaching atmospheric, but a much higher temperature than the gases that enter through the flow path 15. Thus, it will be observed that the seals surrounding the low pressure flow path 16 must effectively seal to prevent leakage of high pressure air from flow path 15 and that temperature gradients exist across the seal members. In addition, the direction of flow differs. Flow through the path 15 passes in a direction extending generally out of the plane of the figure while the flow through the path 16 is in an inward direction. The seal 11 must function efficiently in spite of these extremely different conditions.

The seal piece 12, as has been noted, consists of a subassembly made up of a plurality of parts. These parts are best shown in FIG. 2. The parts consist of a first annular shaped element 17 having a wear resistance coating 18 formed on one of its faces. It is the coated face 18 that sealingly engages the rotating core. Preferably, the piece 17 is relatively thin so that it may flex under temperature variations, spring loading and gas pressure to insure a good seal around its entire periphery in spite of surface irregularities. A first cantilevered spring piece 19 is affixed to the piece .17 at one of its ends. The piece 19 is arcuate in shape and its outer periphery lies on substantially the same circumference as the outer periphery of the piece 17. A second cantilevered spring 21 is affixed to the spring 19 and to the seal piece 17. The spring 21 has an outer periphery that lies on a smaller diameter than the spring 19 and is slightly stiffer than the spring 19. The peripheral edges of the springs 19 and 21 engage the fixed housing and effect a seal with it. In addition, they resiliently bias the piece 17 and particularly its coated surface 18 into sealing engagement with the rotating core of the regenerator. The end of the spring 21 is beveled locally, as at 20, to reduce its thickness so as to not interfere with the sealing of the element 19 with the regenerator housing.

The seal piece 13 has a cross sectional configuration substantially the same as the seal piece 12. This construction is best shown in FIG. 3 and comprises a first thin and flexible part 22 having a face that is provided with a wear resistant coating 23 of any suitable type. First and second cantilevered leaf springs 24 and 25, respectively, are affixed to the part 22 in any suitable manner. The spring 24 is longer than the spring 25 and is more resilient. The outer peripheries of the springs 4 24 and 25 engage the engine housing to effect a seal. The springs 24 and 25 further urge the coating 23 into sealing engagement with the rotating core of the regenerator. The end of the spring 25, like the spring 21 is beveled, as at 30, so as not to interfere with the sealing action of the spring 24.

The spring 25 is formed with a plurality of uniformly spaced notches 26 (FIG. 1). The notches 26 are believed to eliminate the possibility of trapped gas pockets and resultant poor sealing. In addition, they are believed to eliminate a rippling of the lighter spring 24 through its engagement with the spring 25. As with the spring piece 12 the part 22 is relatively thin and flexible so that it may conform to the surface against which it seals under the influence of the springs 24 and 25.

The seal piece 14 has a cross sectional configuration as shown in FIG. 4. This seal piece includes a generally arcuate shaped thin and flexible part 27 having a face to which is applied a wear resistant coating 28. A single cantilevered spring 29 is affixed in a suitable manner of the part 27 and resiliently biases the coating 28 into sealing engagement with the rotating core. The outer peripheral edge of the spring 29 lies on substantially the same diameter as the outer pheriphery of the part 27 and sealingly engages the regenerator housing. It should be noted that the seal piece 14 experiences a smaller pressure differential on its opposite sides than does the seal piece 12. For this reason only a single light cantilevered spring is employed as opposed to the dual spring arrangement used on the seal pieces 12 and 13.

The seal pieces 12, 13 and 14 are constructed so as to be interrelated at their adjacent ends to form what may be considered a lose assembly. That is, the seal piece ends are all interrelated so as to preclude gas leakage.

This interrelationship, however, permits each of the seal pieces to undergo thermal expansion independently of the others. A pair of inwardly facing hooks 31 and 32 are affixed to the part 22 of the seal piece 14 on each of its ends. These hooks 31 and 32 extend into complementary shaped pockets 33 and 34 formed in a pair of pieces 35 and 36 that are connected to the ends of the part 17 of the seal piece 12. The construction of this arrangement is best shown in FIGS. 5 and 6 of the drawings. It will be noted that the pockets 33 and 34 are considerably larger than the hooks 31 and 32 so as to permit some freedom of movement between the adjacent ends of the seal pieces 12 and 14. There is a greater clearance at the end where the hook 32 enters the pocket 34 than at the opposite end, assuming that the rotating core rotates in a clockwise direction as viewed in FIG. 1. This greater clearance is provided in the direction of core rotation so as to permit the rotation to take up some of the clearance between these elements. A tight fit is not desired, however, so as to permit the seal piece 12, which experiences the greater temperature, to undergo thermal expansion relative to the seal piece 14.

The part 22 of the seal piece 33 has an outwardly extending ear 39 at each of its ends that overlies the respective pockets 33 and 34 and which maintains the hooks 31 and 32 from axial preparation from these pockets. Each of the ears 39 is formed with elongated slot 41 that is adapted to receive a smaller diameter pin (not shown) that is fixed to the housing of the associated engine. The entry of the pins into the slots 41 locates the seal piece 13. The fit is sufficiently lose, however, so as to permit free thermal expansion.

' The pieces 35 and 36 are formed with outwardly extending ears 42 that underlie the ears 41 of the seal piece 13. The ears 42 are also formed with elongated slots 43 that register with the slots 41. The aforedescribed pins also enter into the slots 43 so as to locate the seal piece 13 relative to the engine housing.

It should be noted that the leaf springs 19 and 21 of the seal piece 12 and the leaf spring 29 of the seal piece 14 have a generally conical configuration due to the annular shape of these seal pieces. On the other hand, the springs 24 and 25 of the seal piece 13 are disposed at .an angle and lie substantially in a plane. In order to provide effective sealing at the juncture between the seal piece ends, the cantilevered spring 24 of the seal piece 13 is formed with slotted portions 44 at each of its ends. From these slotted portions, the spring 24 is formed with an offset tab like piece 45. The piece 45 is the shape of a segment of a cone and is complementary to the shape of the adjacent ends of the spring 19 of the seal piece 12. Affixed to this offset portion of each of the tabs 45 is a slide 47 (FIG. 7). The slide 47 receives the end portions 48 of the spring 19 of the seal piece 12. The spring 21 of the seal piece 12 is provided with tab like extensions 49 that overlie the outer surface of the spring 24 of the seal piece 13 (FIG. 7 This interconnection permits free movement in all but the axial directions. Thus, the seal pieces are permitted to undergo different thermal expansion while a good seal is maintained at their junctures.

From the described construction it should be clear that each of the seal pieces 12, 13 and 14 is free to expand under the effects of temperature variations independently of the other seal pieces. An effective seal is, however, provided at the juncture of the seal pieces. Thus, the different temperature conditions existing in the flow path 15 and 16 may induce different thermal expansions of the respective seal pieces without causing warping and the attendant lack of good sealing. In additionythe cantilevered spring arrangement which has been described provides the necessary spring loading for the seal against the rotating element and further effects a good seal at the tips of the cantilevered springs with the associated housing. Furthermore, each of the parts of the seal pieces is relatively flexible so that the seal pieces may readily deflect to provide a good seal with the associatedengine parts regardless of surface irregularities in these parts.

.The flexibility or compliance of the seal pieces '12, 13 and 14 has been found to be an important feature in providing effective sealing action under the thermal and other stresses. Previously proposed seals for this type of application have not been compliant for several reasons, the prime reason being the necessity for providing a relatively thick metal substrate on to which the wear resistant coating of the seals was depositedfiThe method by which the seal pieces and particularly the parts or elements 17, 22 and 27 are coated, in accordance with this invention, permits the use of a thin and compliant substrate. Furthermore, the method employed for coating these surfaces can be used to coat the seal after each of the individual pieces is assembled. This reduces the likelihood of damage to the coating. This method will now be described.

Each of the seal pieces 12, 13 and 14 is assembled before the respective coatings 18, 23 and 28 are applied. The assembly is made in such a way that all of the necessary heat treating steps are employed before assembly. The substrates 17, 22 and 27 to which the coating is applied areformed from relatively thin sheet 1 pieces is performed and preferably vacuum heat treatment is desired although the heat treatment may be performed in a protective atmosphere. During the last stage in the heat treatment of the substrates 17, 22 and 27, which may be either precipitation hardening, aging or tempering, the furnace atmospheres are adjusted to form a thin, tightly adhering layer of oxides.

In connection with the previously proposed coating methods, it was thought necessary to completely remove the surface oxides. It has been found, however, that the maintenance of a light surface oxide gives rise to a better coating than if a clean surface was used. It is thought that an exothermic reaction occurs, as will be described, which improves in the bonding. Furthermore, the oxides were previously" removed by shot blasting or similar processes that cause surface stresses and distortions. v i

The oxidized surface maybe rubbed lightly with .emery cloth to remove loose oxide materials. Any organic material present can be removed by an oil free solvent such as trichlorethylene.

Each of the complete seal pieces 12, 13 and 14 is then clampedor otherwise restrained in a suitable fixture via the cantilevered springs so thatthe surfaces of the elements 17, 22 and 27 to be coated are exposed, unobstructed and flat. Each of the fixtured seal pieces is then preheated by placing it in an oven or by preheating it with a plasma spray torch, with the powder feed shut off, to a temperature in the range of 200 to 300 degrees fahrenheit. Higher temperatures may be used but temperatures in this range have been found to give good results while reducing heating time,power requirements and handling difficulties.

After the surface is preheated a transition coating of a reactive material such as nickel aluminide is deposited directly on the surface of the element 17, 22 and 27 by a plasma spray technique. During this operation the respective seal element is moved or rotated rapidly with respect to the spray equipment at a surface velocity of approximately 300 feet per minute. The transition coating causes an exothermic reaction with the surface oxidized to provide an extremely good surface bond. To prevent surface distortion, a cooling'air spray is passed across the surface of the seal elements 12, 13 and 14 to maintain the temperature approximately constant in the 'afor'enoted range. This procedure is followed until a very thin coating of the transition material is applied. In one embodiment when the substrate has a thickness of 0.030 to 0.40 inches a maximum transition coating of 0.003 inches is applied.

'While the workpiece is still at an elevated temperature a wear resistant coating 18., 23 and 28 is applied to the transition coating of the respective seal piece 12, 13 and 14 by a hot spray technique or any other known technique. The wear resistant coating may be of metal oxides and may include additives such as metal fluorides. In a preferred embodiment of the invention, the nominal thickness of the coating is 0.02 inches. During this coating process, the workpiece temperature is again maintained by the use of cooling air jets.

Because of the low temperatures used it has been found unnecessary to permit cooling of the coated parts in the fixture in which they were held during the coating process. After removal and cooling of the coated assemblies a light lapping operation may be employed to insure good surface finish. Only light spring pressure is required during such a lapping process.

in the embodiment of the invention described, a hook and eye arrangement was provided for locating the ends of the seal pieces 12 and 14 relative to each other. In some embodiments, it is not necessary to provide any direct interrelationship between the various seal pieces. That is, the ends of the seal pieces may be located or interrelated relative to each other externally as in the embodiment shown in FIGS. 8 through 10, which willnow be described in detail.

FIG. 8 is a view, in part similar to FIG. and shows a second embodiment of this invention which embodiment is identified generally by the reference numeral 71. The seal 71 is made up of seal pieces 72, 73 and 74, which seal pieces conform generally in shape and construction to the seal pieces l2, l3 and 14, respectively, of the preceding embodiment. Because of these similarities, a detailed description of the individual seal pieces 72, 73 and 74 will not be given nor will the description of the method for coating each of the seal pieces with the wear resistant surface be repeated.

The seal piece 72 includes a first element 75 on which a wear resistant coating 76 is applied in the manner previously described. The coating 76 sealingly engages a housing element 77 of the gas regenerator. ln a like manner, the seal piece 73 has a first part 78 on which a wear resistant coating 79 is deposited. The coating 79 also engages the surface of the housing 77. In a like manner, the seal piece 74 has an element 81 on which a wear resistant coating 82 is deposited. This coating 82 also engages the housing 77. A structure is provided adjacent the juncture of the ends of each of the seal pieces 72, 73 and 74 for interrelating these ends relative to the housing 77. This construction includes an ear 83 that is integrally formed on the element 78 of the seal 73. The ear 83 is formed with an elongated opening 84 that passes a locating pin 85 that is staked relative to the housing 77. The opening 84 is sized so as to permit relatively free movement of the seal piece 73 relative to the housing 77 under the influences of thermal expansion.

A piece 86 having an ear portion is affixed to the element 81 of the seal piece 74 and overlies the integral ear 83 of the seal piece 73. The piece 86 is also formed with an elongated opening 87 that receives the pin 85 with clearance so as to locate the seal piece 74 with respect to the housing 77 and with respect to the remaining seal pieces.

A piece 88 is affixed to the element 75 of the seal piece 72 and has an ear portionthat overlies the ear portion of the piece 86 and the integral ear 83 of the seal piece 73. The ear of the piece 88 is formed in an offset portion 89 and defines an elongated opening 91 through the pin 85 for locating the piece 72 in the manner previously described. The offset of the portion 89 is slightly greater than the thickness of the piece 87 was to permit some axial movement of the seal piece 8 73 relative to the seal piece 72. This is necessary to compensate for variations in the thickness of the coating on these pieces.

, The seal 71 has the same advantages of the previously described seal and these advantages will not be repeated.

It is to be understood that the foregoing description is that of preferred embodiments of the invention. Various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.

We claim:

I. The method of applying a wear resistant coating to a metal substrate for forming a compliant seal comprising the steps of forming a metal oxide layer on the portion of the substrate to be coated, depositing a transition coating of nickel aluminide on the oxidized surface, the transition coating of nickel aluminide being capable of exothermically reacting with the metal oxide layer to form an effective surface bond, exothermically reacting the nickel aluminide transition coating with the metal oxide layer and depositing a wear resistant metal oxide coating on the transition coating.

2. The method of applying a wear resistant coating as set forth in claim 1 further including the step of preheating the substrate prior to depositing of the transition coating thereon.

3. The method of applying a wear resistant coating as set forth in claim 2 further including the step of maintaining the temperature of the substrate within a predetermined range during the exothermic reaction of the transition coating with the oxidized surface.

4. The method of applying a wear resistant coating as set forth in claim 1 wherein the transition coating and wear resistant coatings are deposited by a flame spray technique.

5. The method of applying a wear resistant coating as set forth in claim 4 further including the step of preheating the substrate prior to depositing of the transition coating thereon.

6. The method of applying a wear resistant coating as set forth in claim 5 wherein the substrate is preheated to a temperature in the range of 200 to 300 degrees fahrenheit.

7. The method of applying a wear resistant coating as set forth in claim 6 further including the step of maintaining the temperature of the substrate within a predetermined range during the exothermic reaction of the transition coating with the oxidized surface.

8. The method of applying a wear resistant coating as set forth in claim 1 further including the step of affixing a cantilevered spring to the substrate prior to the coating thereof and holding the assembled spring and substrate against movement during the coating process.

9. The method of applying a wear resistant coating as set forth in claim 8 wherein the wear resistant coating is applied to the substrate to a thickness in the range of one to one and one half times the thickness of the substrate i i l 

1. THE METHOD OF APPLYING A WARD RESISTANT COATING TO A METAL SUBSTRATE FOR FORMING A COMPLIANT SEAL COMPRISING THE STEPS OF FORMING A METAL OXIDE LAYER ON THE PORTION OF THE SUBSTRATE TO BE COATED, DEPOSITING A TRANSTION COATING OF NICKEL ALUMINIDE ON THE OXIDIZED SURFACE, THE TRANSITION COATING OF NICKEL ALUMINIDE BEING CAPABLE OF EXOTHERMICALLY REACTING WITH THE METAL OXIDE LAYER TO FORM AN EFFECTIVE SURFACE BOND, EXOTHERMICALLY REACTING THE NICKEL ALUMINIDE TRANSITION COATING WITH THE METAL OXIDE LAYER AND DEPOSITING A WEAR RESISTANT METAL OXIDE COATING ON THE TRANSITION COATING.
 2. The method of applying a wear resistant coating as set forth in claim 1 further including the step of preheating the substrate prior to depositing of the transition coating thereon.
 3. The method of applying a wear resistant coating as set forth in claim 2 further including the step of maintaining the temperature of the substrate within a predetermined range during the exothermic reaction of the transition coating with the oxidized surface.
 4. The method of applying a wear resistant coating as set forth in claim 1 wherein the transition coating and wear resistant coatings are deposited by a flame spray technique.
 5. The method of applying a wear resistant coating as set forth in claim 4 further including the step of preheating the substrate prior to depositing of the transition coating thereon.
 6. The method of applying a wear resistant coating as set forth in claim 5 wherein the substrate is preheated to a temperature in the range of 200 to 300 degrees fahrenheit.
 7. The method of applying a wear resistant coating as set forth in claim 6 further including the step of maintaining the temperature of the substrate within a predetermined range during the exothermic reaction of the transition coating with the oxidized surface.
 8. The method of applying a wear resistant coating as set forth in claim 1 further including the step of affixing a cantilevered spring to the substrate prior to the coating thereof and holding the assembled spring and substrate against movement during the coating process.
 9. The method of applying a wear resistant coating as set forth in claim 8 wherein the wear resistant coating is applied to the substrate to a thickness in the range of one to one and one half times the thickness of the substrate. 